Zinc alloy coated steel sheet having good sealer adhesion and corrosion resistance and process of manufacturing the same

Abstract

There is provided a zinc alloy coated steel sheet including a vacuum deposited layer capable of improving corrosion resistance and sealer adhesion that are suitable for the use in automobiles, and a process of manufacturing the same. The zinc alloy coated steel sheet includes a zinc coating layer formed on a steel sheet; and a zinc/metal alloy deposited layer formed on the zinc coating layer, wherein the zinc coating layer, and a metal diffusion layer is present in the zinc coating layer.

The invention claimed is: 
     
       1. A process of manufacturing a zinc alloy coated steel sheet having good sealer adhesion and corrosion resistance, the method comprising:
 depositing a zinc/metal alloy coating layer onto a zinc coated steel sheet of an electro-galvanized steel sheet or a hot-dip galvanized steel sheet to form a layered coating where the zinc/metal alloy coating layer is present at an outermost surface of the coating; and 
 thermally treating the zinc coated steel sheet having the layered coating with the zinc/metal alloy coating layer at the outermost surface at a temperature from 250 degrees Celsius (° C.) or above to less than 300° C. for 3 to 100 seconds, 
 wherein depositing the zinc/metal alloy coating layer is carried out with an alloy material composed of 90-95% by weight of at least one conductive metal selected from the group consisting of Mg, Al, Mn, Cr, Cu, Ti, and Ni, and 5-10% by weight of Zn in a vacuum chamber by using a physical vapor deposition (PVD) method using an electrostatic levitator, and the zinc/metal alloy coating layer has a gradient zinc content decreasing from a surface of the zinc coated steel sheet, 
 wherein, the thermally treated zinc alloy coated steel sheet comprises a zinc coating layer formed on a steel sheet and a zinc/metal alloy layer formed by the diffusion of the metal on the zinc coating layer, and 
 a zinc/iron alloy phase is not present in an interface between the steel sheet and the zinc coating layer. 
 
     
     
       2. The process of  claim 1 , wherein the depositing of the zinc/metal alloy onto the zinc coated steel sheet is performed by levitation of a zinc/conductive metal alloy under a vacuum of 1×10 −2  to 1×10 −5  mbar by using an AC magnetic field. 
     
     
       3. The process of  claim 2 , wherein a zinc coating layer has a thickness of 1.4 to 5 micrometers, the zinc/metal alloy deposited layer has a thickness of 0.1 to 1 micrometers, and a zinc/metal alloy layer formed between the zinc coated layer and zinc/metal alloy deposited layer by the thermal treatment extends into the zinc coating layer and the zinc/metal alloy deposited layer. 
     
     
       4. The process of  claim 1 , wherein a zinc coating layer has a thickness of 1.4 to 5 micrometers, the zinc/metal alloy deposited layer has a thickness of 0.1 to 1 micrometers, and a zinc/metal alloy layer formed between the zinc coated layer and zinc/metal alloy deposited layer by the thermal treatment extends into the zinc coating layer and the zinc/metal alloy deposited layer. 
     
     
       5. A process of manufacturing a zinc alloy coated steel sheet having good sealer adhesion and corrosion resistance, the method comprising:
 depositing a zinc/metal alloy onto a zinc coated steel sheet of an electro-galvanized steel sheet or a hot-dip galvanized steel sheet to form a zinc/metal alloy deposited layer; and 
 thermally treating the zinc coated steel sheet with the zinc/metal alloy deposited layer at a temperature from 250 degrees Celsius (° C.) or above to less than 300° C. for 3 to 100 seconds, 
 wherein depositing the zinc/metal alloy coating layer is carried out with an alloy material composed of 90-95% by weight of at least one metal and 5-10% by weight of Zn in a vacuum chamber by using a physical vapor deposition (PVD) method using an electrostatic levitator, and the zinc/metal alloy coating layer has a gradient zinc content decreasing from a surface of the zinc coated steel sheet, 
 wherein the thermally treated zinc alloy coated steel sheet comprises a zinc coating layer formed on a steel sheet and a zinc/metal alloy layer formed by the diffusion of the metal on the zinc coating layer, 
 a zinc/iron alloy phase is not present in an interface between the steel sheet and the zinc coating layer, and the metal is selected from the group consisting of Al, Mn, Cr, Cu, Ti, and Ni.